IT201900017531A1 - METHOD OF CONTROL OF A ROAD VEHICLE WITH A MICROSLITTING OF THE CLUTCH - Google Patents

Description

DESCRIPTION

of the patent for industrial invention entitled:

"METHOD OF CONTROL OF A ROAD VEHICLE WITH A MICROSLITTING OF THE CLUTCH"

TECHNIQUE SECTOR

The present invention relates to a control method for a road vehicle.

The present invention finds advantageous application to a transmission equipped with a double clutch servo-assisted gearbox, to which the following discussion will make explicit reference without thereby losing generality.

ANTERIOR ART

A transmission equipped with a double clutch servo-assisted gearbox includes a pair of coaxial primary shafts, independent and inserted one inside the other; two coaxial clutches, each of which is adapted to connect a respective primary shaft to a driving shaft of an internal combustion engine; and at least one secondary shaft which transmits motion to the driving wheels and can be coupled to the primary shafts by means of respective gears, each of which defines a gear.

During a gear change, the current gear couples the secondary shaft to a primary shaft while the next gear couples the secondary shaft to the other primary shaft; consequently, the gear change takes place by crossing the two clutches, that is, opening the clutch associated with the current gear and at the same time closing the clutch associated with the next gear.

It has been observed that when the tires of the drive wheels are close to the grip limit (usually when a low gear is engaged in the gearbox and the grip of the road surface is precarious, for example due to the presence of water), a phenomenon called "stick-slip" which is characterized by continuous and subsequent loss and recovery of grip; in other words, for a short distance the tire of a driving wheel adheres to the ground, for the next section the tire loses grip and slips, for a further subsequent section the tire regains grip and so on.

The phenomenon called "stick-slip" is negative as it triggers oscillations in the transmission that are transmitted to the internal combustion engine which in turn transfers them to the frame through the pads with which the internal combustion engine is fixed to the frame. The oscillations triggered by the phenomenon called "stickslip" almost always cause a metallic noise that is particularly annoying for the driver (making it seem that there is something broken in the road vehicle); moreover, in some particularly unfortunate conditions the oscillations triggered by the phenomenon called "stick-slip" can be amplified by structural resonances to generate torque peaks that can damage the components of the transmission and of the internal combustion engine (generating breakage due to fatigue after a certain time or even generating sudden breaks following a particularly intense impulsive solicitation).

DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a control method for a road vehicle, which control method allows to avoid the negative consequences of the phenomenon called "stick-slip" described above and, at the same time, is easy and economical to implement.

According to the present invention, a method of controlling a road vehicle is provided, according to what is claimed by the attached claims.

The claims describe preferred embodiments of the present invention forming an integral part of the present description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the attached drawings, which illustrate a non-limiting example of embodiment, in which:

Figure 1 is a schematic and plan view of a rear-wheel drive road vehicle equipped with a transmission with a double-clutch servo-assisted gearbox which is controlled according to the control method of the present invention;

Figure 2 is a schematic view of the transmission of figure 1; And

Figure 3 is a block diagram of a control logic implemented in a transmission control unit.

PREFERRED FORMS OF IMPLEMENTATION OF THE INVENTION

In Figure 1, the number 1 indicates as a whole a road vehicle (in particular a car) provided with two front driven (ie non-driving) wheels 2 and two rear driving wheels 3. An internal combustion engine 4 is arranged in the front position, which is provided with a drive shaft 5 and produces a driving torque which is transmitted to the driving wheels 3 by means of a transmission 6. The transmission 6 comprises a servo-assisted gearbox 7 with double clutch arranged at the rear and a transmission shaft 8 which connects the drive shaft 5 to an input of the double clutch servo-assisted gearbox 7. A self-locking differential 9 is connected in cascade to the double-clutch servo-assisted gearbox 7, from which a pair of half-shafts 10 depart, each of which is integral with a drive wheel 3.

The road vehicle 1 comprises a control unit 11 for the control of the engine 4 which supervises the control of the engine 4, a control unit 12 for the control of the transmission 6 which supervises the control of the transmission 6, and a bus line 13, which is for example made according to the CAN (Car Area Network) protocol is extended to the entire road vehicle 1 and allows the control units 11 and 12 to communicate with each other. In other words, the engine control unit 11 4 and the transmission control unit 12 6 are connected to the BUS line 13 and therefore can communicate with each other by means of messages forwarded on the BUS line 13 itself. Furthermore, the engine control unit 11 4 and the transmission control unit 12 6 can be directly connected to each other by means of a dedicated synchronization cable 14, which is capable of transmitting directly from the transmission control unit 12 6 to the engine control unit 11 4 a signal without the delays introduced by the BUS line 13. Alternatively, the synchronization cable 14 may not be present and all communications between the two control units 11 and 12 are exchanged using the BUS line 13.

As shown in Figure 2, the double clutch servo-assisted gearbox 7 includes a pair of primary shafts 15 coaxial to each other, independent and inserted one inside the other. In addition, the double-clutch servo-assisted gearbox 7 includes two coaxial clutches 16, each of which is designed to connect a respective primary shaft 15 to the drive shaft 5 of the internal combustion engine 4 by interposing the transmission shaft 8; each clutch 16 is in an oil bath and is therefore commanded under pressure (i.e. the degree of opening / closing of the clutch 16 is determined by the oil pressure inside the clutch 16 itself); according to an alternative embodiment, each clutch 16 is dry and is therefore controlled in position (ie the degree of opening / closing of the clutch 16 is determined by the position of a movable element of the clutch 16 itself). The double clutch servo-assisted gearbox 7 comprises a single secondary shaft 17 connected to the differential 9 which transmits motion to the driving wheels 3; according to an alternative and equivalent embodiment, the double clutch servo-assisted gearbox 7 comprises two secondary shafts 17 both connected to the differential 9.

The dual clutch 7 power-assisted gearbox has seven forward gears indicated with Roman numerals (first gear I, second gear II, third gear III, fourth gear IV, fifth gear V, sixth gear VI and seventh gear VII) and a reverse gear (indicated with the letter R). The primary shaft 15 and the secondary shaft 17 are mechanically coupled to each other by means of a plurality of gears, each of which defines a respective gear and comprises a primary toothed wheel 18 mounted on the primary shaft 15 and a secondary toothed wheel 19 mounted on the 17 secondary shaft. To allow correct operation of the double clutch power-assisted gearbox 7, all the odd gears (first gear I, third gear III, fifth gear V, seventh gear VII) are coupled to the same primary shaft 15, while all the even gears (second gear II, fourth gear IV, and sixth gear VI) are coupled to the other primary shaft 15.

Each primary toothed wheel 18 is keyed to a respective primary shaft 15 to always rotate integrally with the primary shaft 15 itself and permanently meshes with the respective secondary toothed wheel 19; instead, each secondary toothed wheel 19 is mounted idle on the secondary shaft 17. Furthermore, the double clutch servo-assisted gearbox 7 comprises four double synchronizers 20, each of which is mounted coaxially to the secondary shaft 17, is arranged between two secondary toothed wheels 19, and is adapted to be actuated to alternately engage the two respective wheels 19 secondary toothed wheels to the secondary shaft 17 (ie to alternatively make the two respective secondary toothed wheels 19 angularly integral with the secondary shaft 17). In other words, each synchronizer 20 can be moved in one direction to engage a secondary toothed wheel 19 to the secondary shaft 17, or it can be moved in the other direction to engage the other secondary toothed wheel 19 to the secondary shaft 17.

The double clutch gearbox 7 comprises a single secondary shaft 17 connected to the differential 9 which transmits motion to the driving wheels 3; according to an alternative and equivalent embodiment, the double clutch gearbox 7 comprises two secondary shafts 17 both connected to the differential 9.

According to what is illustrated in Figure 1, the road vehicle 1 comprises a passenger compartment in which a driving position intended for the driver is arranged; the driving position comprises a seat (not shown), a steering wheel 21, an accelerator pedal 22, a brake pedal 23, and two paddles 24 and 25 which control the double clutch power-assisted gearbox 7 and are connected on both sides of the steering wheel 21. The ascending paddle 24 is operated by the driver (by briefly pressing) to request an ascending gear change (i.e. the engagement of a new gear ratio longer than the current gear ratio and contiguous to the gear ratio current), while the descending vane 25 is operated by the driver (by means of a short press) to request a downshift (i.e. the engagement of a new gear ratio shorter than the current gear ratio and contiguous to the current gear ratio ).

In use, the transmission control unit 12 6 checks whether the tires of the driving wheels 3 are close to a grip limit and then opens (slightly) the clutch 16 so that the clutch 16 transmits a driving torque to the driving wheels 3 with a constant and non-zero slip of the clutch 16. In other words, due to the effect of this slippage, a driving disc 26 of the clutch 16 (schematically illustrated in Figure 2) has a rotation speed ω1 higher than a rotation speed ω2 of a driven disc 27 of the clutch 16 (schematically illustrated in Figure 2). ); therefore the slippage of the clutch 16 is (in absolute value) equal to the difference between the rotation speed ω1 of the driving disc 26 of the clutch 16 and the rotation speed ω2 of the driven disc 27 of the clutch 16.

Generally, the slippage of the clutch 16 (i.e. the difference between the rotation speed ω1 of the driving plate 26 and the rotation speed ω2 of the driven plate 27) is included in absolute value between 70 and 180 rpm and is included in relative value between 0.5% and 1.2% of a rotation speed ωE of the internal combustion engine 4.

The transmission control unit 12 6 considers that the tires of the driving wheels 3 are close to the grip limit if three conditions occur simultaneously:

1. in the power-assisted gearbox 7 a gear belonging to a predetermined set of gears is engaged (which comprises the lowest gears or generally the first gear I, the second gear II and the third gear III);

2. the rotation speed ωE of the internal combustion engine 4 is comprised in a predetermined speed range (for example between 4,000 and 8,000 rpm); and

3. an engine torque TE generated by the internal combustion engine 4 is higher than a torque threshold value.

According to a possible embodiment, the torque threshold value is always constant. Alternatively, the transmission control unit 12 6 could determine a degree of adhesion of a road surface on which the road vehicle 1 rests and therefore could determine from time to time the torque threshold value as a function of the degree of adhesion of the road surface. road; generally, information on the degree of grip of the road surface is available on bus line 13 as it is estimated (in a known way) and shared by a brake control unit.

According to a possible embodiment schematically illustrated in Figure 3, the transmission control unit 12 determines an objective slip ST of the clutch 16, cyclically determines an effective slip SR of the clutch 16, detects the engine torque TE generated by the combustion engine 4 internal, establishes a TC clutch torque that must be transmitted by the clutch 16 and is (slightly) lower than the engine torque TE, drives the clutch 16 to transmit the clutch TC torque, and cyclically varies the clutch TC torque according to a difference between the target ST slip of clutch 16 and actual SR slip of clutch 16.

In other words, the transmission control unit 12 6 varies the clutch torque TC to follow the target slip ST of the clutch 16, that is, to make the clutch 16 always present the target slip ST.

It is important to note that the TC clutch torque is converted into a corresponding pressure value by means of a conversion table (known a priori) as the clutches 16 are controlled under pressure (of the oil).

According to the embodiment illustrated in Figure 3, the transmission control unit 12 implements a feedback control to modulate the TC clutch torque; in the feedback control the control error εS is equal to the difference between the objective slip ST of the clutch 16 and the actual slip SR of the clutch 16. In particular, the feedback control involves the use of a subtractor block 28 which calculates the 'control error εS by making the difference between the objective slip ST of the clutch 16 and the effective slip SR of the clutch 16 and also involves the use of a 29 PID controller which receives the control error εS in input and outputs the torque TC clutch with which to drive the clutch 16. According to what is illustrated in Figure 3, a calculation block 30 is provided which calculates the effective slip SR of the clutch 16 by making the difference between the rotation speed ω1 of the driving disc 26 and the speed ω2 rotation of the driven disc 27.

The PID controller 29 also receives the engine torque TE generated by the internal combustion engine 4, since the clutch torque TC is determined starting from the engine torque TE; in fact, the clutch TC torque must be (slightly) lower than the engine TE torque.

In other words, the control mode described above provides for managing the effective SR slip of the clutch 16 with micro-variations of the clutch TC torque while maintaining constant (obviously as long as the driver's action on the accelerator pedal 22 is constant) TE engine torque generated by internal combustion engine 4. This control mode (which involves only the clutch 16 and not the internal combustion engine 4) is effective (i.e. it is able to make the clutch 16 always work in a small neighborhood of the objective ST slip), but on the other hand it tends to transmit to the drive wheels 3 an oscillating torque (since the torque TC clutch transmitted by the clutch is continuously variable) which could cause longitudinal oscillations on the motion of the road vehicle 1 which can be felt by the driver.

To avoid this inconvenience (i.e. to keep the torque transmitted to the drive wheels 3 more constant), the transmission control unit 12 could operate in a different way, i.e. the transmission control unit 12 determines the objective slippage ST of the clutch 16 , detects the engine torque TE generated by the internal combustion engine 4, establishes the clutch torque TC that must be transmitted by the clutch 16 equal to the engine torque TE (and therefore constant until the driver acts differently on the accelerator pedal 22) , drives the clutch 16 to transmit the torque TC clutch (which is kept constant until the driver acts differently on the accelerator pedal 22), detects the rotation speed ω2 of the disc 27 driven by the clutch 16, determines a speed ω1 -T of objective rotation of the driving disc 26 of the clutch 16 adding to the rotation speed ω2 of the driven disc 27 of the clutch 16 the slip ST target of the clutch 16, and drives the internal combustion engine 4 to vary (with micro-variations) the engine torque TE generated by the internal combustion engine 4 so as to follow the target rotation speed ω1-T of the clutch drive disc 26 16.

In other words, this alternative operating mode described above provides for managing the effective SR slip of the clutch 16 with micro-variations of the engine torque TE generated by the internal combustion engine 4, keeping constant (obviously until the driver's action on the accelerator pedal 22) the torque TC clutch.

The embodiments described here can be combined with each other without departing from the scope of protection of the present invention.

The control method described above has numerous advantages.

In the first place, the control method described above allows to avoid the negative consequences of the phenomenon called "stick-slip" (which in itself cannot be avoided under certain conditions), since the torque oscillations introduced into the transmission 6 by the phenomenon called "Stick-slip" are blocked by the clutch 16 which operates with a certain non-zero and constant slip; in other words, when the clutch 16 operates with a certain non-zero and constant slip, the clutch 16 itself acts as a mechanical low-pass filter which effectively and efficiently blocks the torque oscillations introduced into the transmission 6 by the phenomenon called "stick -slip ". Consequently, the torque oscillations introduced into the transmission 6 by the phenomenon called "stick-slip" stop in the clutch 16 and are not transmitted (except in a marginal way and without consequently) to the internal combustion engine 4.

Furthermore, the control method described above is easy and economical to implement since for its execution it requires a limited occupation of memory and a reduced computing power.

LIST OF REFERENCE NUMBERS IN THE FIGURES 1 road vehicle

2 front wheels

3 rear wheels

4 engine

5 crankshaft

6 transmission

7 change

8 drive shaft

9 differential

10 drive shafts

11 engine control unit

12 transmission control unit 13 BUS line

14 sync cable

15 primary trees

16 clutches

17 secondary shaft

18 primary gear wheel

19 secondary gear

20 synchronizers

21 steering wheel

22 accelerator pedal

23 brake pedal

24 ascending vane

25 descending vane 26 conducting disk

27 driven disc

28 subtractor block 29 PID controller

30 calculation block ω1 rotation speed ω2 rotation speed ωE rotation speed SR actual slip ST target slip εS control error TC clutch torque

TE motor torque

Claims (11)

R I V E N D I C A Z I O N I 1) Method of controlling a road vehicle (1) equipped with a clutch (16) which connects an internal combustion engine (4) to driving wheels (3) and is arranged upstream of a power-assisted gearbox (7); the control method includes the steps of: check if the tires of the driving wheels (3) are close to a grip limit; and open the clutch (16) so that the clutch (16) transmits to the driving wheels (3) a driving torque with a constant and non-zero slip of the clutch (16) when the tires of the driving wheels (3) are close to the limit of adherence. 2) Control method according to claim 1, in which, due to the effect of the slipping, a disk (26) driving the clutch (16) has a rotation speed (ω1) higher than a rotation speed (ω2) of a disk (27) clutch pipe (16). 3) Control method according to claim 2, wherein a difference between the rotation speed (ω1) of the driving disc (26) and the rotation speed (ω2) of the driven disc (27) is between 70 and 180 rpm minute. 4) Control method according to claim 2 or 3, wherein a difference between the rotation speed (ω1) of the driving disc (26) and the rotation speed (ω2) of the driven disc (27) is between 0.5 % and 1.2% of a rotation speed (ωE) of the internal combustion engine (4). 5) Test method according to one of claims 1 to 4, wherein the tires of the driving wheels (3) are considered to be close to the grip limit if: a gear belonging to a predetermined set of gears is engaged in the power-assisted gearbox (7); a rotation speed (ωE) of the internal combustion engine (4) is included in a predetermined speed range; and an engine torque (TE) generated by the internal combustion engine (4) is higher than a torque threshold value. 6) Control method according to claim 5 and comprising the further steps of: determining a degree of adhesion of a road surface on which the road vehicle (1) rests; And determine the torque threshold value as a function of the degree of grip of the road surface. 7) Control method according to one of claims 1 to 6 and comprising the further steps of: determining an objective slip (ST) of the clutch (16); cyclically determining an effective slip (SR) of the clutch (16); detecting an engine torque (TE) generated by the internal combustion engine (4); establishing a clutch torque (TC) which must be transmitted by the clutch (16) and is lower than the engine torque (TE); drive the clutch (16) to transmit the clutch torque (TC); And cyclically vary the clutch torque (TC) as a function of a difference between the target slip (ST) of the clutch (16) and the actual slip (SR) of the clutch (16). 8) A control method according to claim 7, wherein the clutch torque (TC) is varied to track the target slip (ST) of the clutch (16). 9) Control method according to claim 7 or 8, wherein the clutch torque (TC) is modulated by a feedback control in which a control error (εS) is the difference between the target slip (ST) of the clutch (16 ) and actual slip (SR) of the clutch (16). 10) Control method according to claim 9, in which the clutch torque (TC) is varied by a PID controller (29) which receives the control error (εS) in input. 11) Control method according to one of claims 1 to 6 and comprising the further steps of: determining an objective slippage (ST) of the clutch (16); detecting an engine torque (TE) generated by the internal combustion engine (4); establishing a clutch torque (TC) to be transmitted by the clutch (16) equal to the engine torque (TE); drive the clutch (16) to transmit the clutch torque (TC); detecting a speed (ω2) of rotation of a disk (27) driven by the clutch (16); determine a target rotation speed (ω1-T) of a clutch drive plate (26) (16) by adding the target slip (ST) of the clutch to the rotation speed (ω2) of the clutch drive plate (27) (16) (16); And drive the internal combustion engine (4) to vary the engine torque (TE) generated by the internal combustion engine (4) in order to follow the target rotation speed (ω1-T) of the disc (26) driving the clutch (16 ).